Processor-based systems use memory devices, such as dynamic random access memory (“DRAM”) devices, to store data (e.g. representing instructions, data to be processed, etc.) that are accessed by the processor. In a typical computer system, the processor communicates with the system memory including the memory devices through a processor bus and one or more memory controllers. In some memory systems, a group of memory devices of the system memory are controlled by an associated memory controller. The processor may provide to the memory controller a memory request including a memory command, such as a read command, and an address designating the location from which data are to be read from memory. The memory controller may use the command and address to generate appropriate memory commands as well as row and column addresses, which may be provided to the memory devices associated with that memory controller. In response to the commands and addresses, data may be transferred between the memory devices and the processor.
A DRAM cell may generally include an access device (e.g. a transistor) and a capacitor for storing charge in the memory cell. Word lines may be connected to groups of memory cells (e.g. rows of memory cells) while digit lines may be connected to other groups of memory cells (e.g. columns of memory cells) such that one memory cell may be addressed by a word and digit line. A signal provided by a word line may activate the access device (e.g. transistors) of the corresponding group of memory cells, for example the word line may be coupled to the gates of access devices. The digit lines may be coupled to the sources or drains of access devices, and may accordingly be driven to a logic high or low voltage (e.g. Vcc or ground) depending on the charge of the memory cell. Sense amplifiers may be used to drive the digit lines. Typically, a pair of digit lines are used for each group (e.g. column) of memory cells. The pair of digit lines may carry complementary signals, and may be precharged to a reference voltage which may be between the logic high and low voltages used to indicate a ‘1’ and ‘0’. Once activated, by a word line control signal, a sense amplifier may then drive the digit lines to respective voltages (e.g. Vcc and ground) depending on the value stored in the memory cell.